Apparatus and method for sealing a wellbore

ABSTRACT

An improved valve for sealing a wellbore and method of use, in particular for prevention of well blow outs. In one embodiment, the apparatus is designed to seal a well through rotation of rams. The rams may be actuated to seal the well without having to work against full well pressure as fluid volumes in the apparatus housing, which also contains the rams, are preserved. This functionality allows the apparatus to be constructed with smaller dimensions than existing prior art blow out prevention valves aiding handling and manoeuvrability. The improved valve according to one embodiment also has a mechanism that guides a wireline or a pipeline being run in the wellbore to the centre of the bore and allows a seal to be formed around the wireline or pipeline.

This application claims priority from United Kingdom (GB) PatentApplication Number 0425117.9 filed on 13 Nov. 2004.

FIELD OF THE INVENTION

The present invention relates to valves, and in particular to animproved valve for use in wireline and wellhead control systems for theoil and gas industry. In one aspect the invention relates to an improvedblow out preventer (BOP).

BACKGROUND OF THE INVENTION

Specialised valves, including blow out preventers (BOPs), have beenavailable for many decades, and provide a means for sealing the wellboreat the wellhead against well pressure if the drilling crew loses controlof formation of fluids or if required to seal a wireline or loggingcable during well service operations. A conventional ram type BOP islocated at the wellhead, and consists of two halves of a cover for thewellbore, located on diametrically opposed sides of the well bore. Thecovers consist of steel rams and elastomeric ram blocks, and aretypically actuated by large diameter hydraulic cylinders located on eachside of the wellbore. If a well control event occurs, the hydrauliccylinders will be remotely actuated to force the rams to enter thewellbore from either side, meeting at the centre to seal against wellpressure below. Importantly, the BOP must have the ability to seal thewellbore without cutting the wireline, allowing subsequent retrieval ofthe toolstring.

The ram blocks will typically have cooperating, shaped surfaces toensure alignment. The ram blocks are available in a variety ofconfigurations, and for applications where pipeline or wireline is beingrun in the well will be provided with a cut-out formation (typically acorresponding pair of semi-circular recesses defining a narrowthroughbore) designed to allow the wireline or pipeline to extendthrough the BOP without damage. The ram blocks will be designed suchthat a tight seal is formed around the pipeline or wireline and aroundthe aperture through which the rams move. The ram blocks will often beprovided with a guide, such that when the rams move from an open to aclosed position, the pipeline or wireline is guided into the centre ofthe wellbore such that it is received in the cut-out formation withoutdamage.

The rams in a typical ram BOP are self-energising, in the sense thatafter they are initially actuated by the hydraulics, well pressure isallowed to get behind a part of the ram, forcing it towards a closedposition. The elastomeric seals of the ram blocks are U shaped inlongitudinal section through the plane which the rams extend, and extendfully across the opening of the wellbore. The U-shaped seals allow thewell pressure to force the seals upward and inward, such that the wellpressure energises the seal and tends to keep the rams in a sealedconfiguration.

Other variations on the ram BOP are available, including rams designedto completely shear through pipe or wireline. In addition, somearrangements are manually operated rather than hydraulically operated.In this case, the actuators normally consist of large screws and arerotated by use of a large handle to generate the torque required todrive the rams against the well pressure.

Presently available ram type BOPs suffer from a number of deficienciesand drawbacks. In particular, many of the drawbacks arise from the sizeof the apparatus. Available designs consist of a pair of rams arrangedperpendicular to the wellbore, and extending on either side of thewellbore by up to 2.5 meters (around 100 inches). This has significantimplications for the construction of well control apparatus at the rig.Ideally, the BOP stack would be located close to the wellhead, tomaximise the height above available to accommodate the toolstring.However, in practice, it is difficult to manoeuvre the BOP stack throughplatforms on the rig structure. A platform on the rig structure wouldtypically have a hole in the grating of around 24 inches diameter(depending on the diameter of pipe passing through). This opening is toosmall to allow a ram-type BOP to be passed through in its usual uprightconfiguration where the hydraulic actuators are oriented horizontally.This requires the BOP to be manoeuvred carefully such that thecross-axis access is oriented vertically, allowing the BOP to be passedthrough the opening. This is a difficult and dangerous operation due tothe size and weight of the BOP stack. A reduction in weight is limitedby the need for large diameter hydraulic rams and high strength steelcomponents.

As an alternative, the platform may be provided with a larger diameterslot to allow the passing of the BOP to be conducted more easily.However, this has implications for the health and safety of personnelworking at the platform, and may require installation railings or otherbarriers to prevent personnel from falling through the slots. It istherefore more usual to install the BOP stack at an elevated heightabove the wellhead, of in excess of 13 meters (40 feet). The consequenceis that a greater overall height of well control apparatus is required,or alternatively restrictions are placed on the length of tool stringavailable. This deficiency is particularly important for concurrentoperations.

Existing BOP designs suffer from other deficiencies. These includeproblems with the structural strength of the ram. The ram blocks locatedon either side of the wellbore will typically include a recess andprotrusion which cooperate to ensure that the ram blocks areappropriately aligned. The recess formed on a ram will reduce thestructural strength in the ram. Moreover, the recess may in fact beformed on an outer surface of the ram, meaning that as the ram issealing it has a portion that is unsupported. The ram is therefore“floating” rather than being fully supported by the body of the BOP.This can also result in deformation of the ram, impacting on itsapplication to high pressure BOPs.

The arrangement of a typical ram BOP can also cause difficulties inguiding the pipeline or wireline to the right part of the ram blockformation (i.e. the cut-out formation). These difficulties arise in partdue to the problems with keying the rams appropriately. In addition,typically the piston assembly on one side of the wellbore will beslightly looser than the opposing ram, resulting in the loose pistonassembly being driven to the full extent of its travel before theopposing piston assembly begins to move. This increases the probabilityof the wireline or pipeline being snagged or damaged by the guidingprofile. This can damage the wireline or pipeline and in severe casescause it to be sheared.

A further deficiency of typical ram-type BOPs is the time taken toactuate the rams, due to the high volume hydraulic cylinders, or worse,the time required to manually close the rams. This has safetyimplications.

The present applicant has identified the need for an improved valvedesign, and in particular an improved BOP design that differssignificantly from a conventional ram type BOP.

It is a first aim of the invention to provide an apparatus suitable forsealing a bore that obviates or at least mitigates some of the drawbacksand deficiencies of available valves and/or BOPs. In particular, it isan aim of at least one aspect of the invention to provide an improvedvalve or BOP for sealing around a wireline, pipeline or conduit in awellbore.

It is a further aim of the invention to provide apparatus for sealing awellbore of reduced external size, and in particular apparatus of lesserlateral dimension and reduced weight when compared with a typical ramtype BOP.

A further aim of the invention is to provide apparatus for sealing awellbore, where the apparatus has a reduced requirement for hydraulicactuation when compared with a typical ram type BOP.

Further aims and objects of the invention will become apparent from thefollowing description.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is providedapparatus for sealing a wellbore, the apparatus comprising a ramassembly having a pair of rams rotatably mounted in a housing andactuating means, the apparatus having a first open position in whichfluid may pass through the wellbore and a second closed position inwhich the rams abut to seal the wellbore, wherein the apparatus is movedbetween the open and closed positions by rotating the rams.

In the context of this description, the word ram should not be taken toimply a linear movement of components, as with conventional ram-typeBOPs. The rams and ram assemblies described herein are analogous to therams in a conventional ram-type BOP in the sense that they move togetherto abut and form a seal. References to rams should be taken to meanassemblies, components, members or blocks which are moveable to aposition in which they form an obstruction in the wellbore.

Preferably, the apparatus has a maximum lateral dimension of 80 cm.

Preferably, the maximum lateral dimension is less than 50 cm.

Preferably, the maximum lateral dimension is less than 40 cm.

According to a second aspect of the invention, there is providedapparatus for sealing a wellbore around a wireline or pipeline being runin the wellbore, the apparatus comprising a ram assembly and actuatingmeans, wherein the apparatus comprises a first position in which thewellbore is open and a second position in which the wellbore is closed,wherein the actuating means causes the ram assembly to rotate from itsfirst open position to its second closed position in which the wellboreis sealed around the wireline or pipeline.

According to a third aspect of the invention there is provided aapparatus for sealing a wellbore, the apparatus comprising a pair oframs moveable from a first position in which the wellbore is open and asecond position in which the rams seal the wellbore around a wireline orpipeline, characterised in that when the apparatus is in its operatingorientation, the apparatus has a maximum lateral dimension which allowsit to pass through an aperture in a rig platform through which thewellhead control equipment passes.

Preferably, the maximum lateral dimension is less half of the maximumlateral dimension of a ram-type BOP operating on an equivalent diameterwellbore at equivalent well pressure.

Preferably, the maximum lateral dimension is less a third of the maximumlateral dimension of a ram-type BOP operating on an equivalent diameterwellbore at equivalent well pressure.

Preferably, the maximum lateral dimension is less than 80 cm.

Preferably, the maximum lateral dimension is less than 50 cm.

Preferably, the maximum lateral dimension is less than 40 cm.

According to a fourth aspect of the invention there is provided aapparatus for sealing a wellbore, the apparatus comprising a pair oframs moveable from a first position in which the wellbore is open and asecond position in which the rams seal the wellbore around a wireline orpipeline, characterised in that when the apparatus is in its operatingorientation, the apparatus has a maximum lateral dimension of less than80 cm.

Preferably, the apparatus comprises a pair of rams rotatably mounted ina housing and actuating means, wherein the apparatus is moved betweenthe open and closed positions by rotating the rams.

According to a fifth aspect of the invention, there is providedapparatus for sealing a wellbore, the apparatus comprising a ramassembly having a pair of rams, and actuating means, the apparatushaving a first open position in which fluid may pass through thewellbore and a second closed position in which the rams abut to seal thewellbore, wherein the rams are moved from the first and second positionswithout substantially changing the volume of the actuating means exposedto well pressure.

Preferably, the apparatus comprises a pair of rams rotatably mounted ina housing and actuating means, wherein the apparatus is moved betweenthe open and closed positions by rotating the rams.

According to a sixth aspect of the invention there is provided a blowoutpreventer comprising a ram assembly having a pair of rams rotatablymounted in a housing, the blowout preventer having a first open positionin which fluid may pass through the wellbore and a second closedposition in which the rams abut to seal the wellbore, wherein the blowout preventer is adapted to be moved between the open and closedpositions by rotating the rams.

The following statements reflect optional features of any of the firstto sixth aspects of the invention.

Optionally, the rams comprise formations for locating a wireline orpipeline in the closed position.

Preferably, the apparatus comprises alignment means for guiding awireline or pipeline towards the centre of the wellbore during rotationof the rams.

More preferably, the apparatus comprises alignment means for guiding awireline or pipeline towards the formations during rotation of the rams.

The alignment means may be a drum adapted to rotate about the axis ofrotation of a ram.

The drum may comprise a throughbore of a first diameter, through whichthe wireline or pipeline extends.

Preferably, the throughbore defines an aperture which decreases in crosssectional area during rotation of the drum.

Preferably, the throughbore is perpendicular to the axis of rotation ofthe drum.

The first diameter is preferably equal to or greater than the innerdiameter of the wellbore.

Preferably, a first opening of the throughbore is provided with achannel formed outwardly from an edge of the throughbore.

More preferably, a second opening of the throughbore is provided with aformation on its edge, diametrically opposed from the channel.

The formation may be a second channel formed outwardly from an edge ofthe throughbore, such that the first an second channels together form anaperture extending through the drum perpendicular to the axis ofrotation.

The aperture may extend through the axis of rotation of the drum.

Preferably, the aperture is aligned with the formations for locating awireline or pipeline in the closed position.

Alternatively, the formation is a cutting edge adapted to shear awireline or pipeline as the apparatus moves to its closed position.

Preferably, each ram comprises a sealing assembly having one or moreelastomeric seals.

More preferably, the sealing assembly comprises an inner seal adapted tocooperate with an inner seal on the opposing ram to seal against thewireline or pipeline.

More preferably, the sealing assembly comprises an outer seal adapted toseal edges of the wellbore against well pressure.

Optionally, the inner seal is retained on the ram by the outer seal.

Preferably, the apparatus is hydraulically actuated.

Optionally, the apparatus is provided with a manual override mechanism.

Alternatively, the apparatus is manually actuated.

According to a seventh aspect of the invention there is provided amethod of configuring pressure control equipment at a rig, the methodcomprising the steps of:

-   -   Providing a blowout preventer at the rig, the blowout preventer        comprising a pair of rams moveable from a first position in        which the wellbore is open and a second position in which the        rams seal the wellbore around a wireline or pipeline;    -   Passing the blowout preventer through an aperture in a rig        platform while the blowout preventer is in its operating        orientation;    -   Installing the blowout preventer on the pressure control        equipment.

According to a eighth aspect of the invention there is provided a methodof sealing a wellbore, the method comprising the step of rotating a pairof rams in a ram assembly from a first open position in which fluid maypass through the wellbore and a second closed position in which the ramsabut to seal the wellbore.

BRIEF DESCRIPTION OF THE DRAWINGS

There will now be described, by way of example only, embodiments of theinvention with reference to the following drawings, of which:

FIG. 1 is a front view of a blow out preventer (BOP) stack in accordancewith an embodiment of the invention;

FIG. 2 is a view of the BOP stack of FIG. 1 from a first side, showinglongitudinal section through the actuating means;

FIG. 3 is a plan view of the apparatus of FIG. 1;

FIG. 4 is a perspective view of the embodiment of FIG. 1, showing themain body of the BOP being partially transparent to display internalcomponents;

FIG. 5A is a perspective view from one side and above of the ramassembly in accordance with an embodiment of the invention, shown in itsopen position;

FIG. 5B is a perspective view from above and one side of the ramassembly of FIG. 5A, shown in its closed position;

FIG. 6A is a perspective view of a ram of the embodiment of FIGS. 4 and5;

FIGS. 6B and 6C are perspective views of an alignment drum of theembodiments of FIGS. 4 and 5;

FIG. 6D is a perspective view of a ram key plate of the embodiment ofFIGS. 4 and 5;

FIG. 7A is a perspective view of an outer seal of a sealing assemblyused with an embodiment of the invention;

FIG. 7B is a perspective view of an inner seal of a sealing assemblyused with an embodiment of the invention;

FIG. 8A is a plan view of the ram assembly of the embodiments of FIGS. 4and 5 in a fully open position;

FIG. 8B is a plan view of the embodiment of FIG. 5 in a partially closedposition;

FIG. 8C is a plan view of the ram assembly of the embodiment of FIG. 5in a partially open position;

FIG. 8D is a plan view of the ram assembly of FIG. 5 in a fully closedposition;

FIGS. 9A and 9B are perspective views of an alignment drum in accordancewith an alternative embodiment of the invention;

FIGS. 10A and 10B are perspective views of the alignment drum of FIGS.9A and 9B in a ram assembly in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION

Referring firstly to FIGS. 1 to 4, a first embodiment of the apparatusof the invention is shown, implemented as a blow out preventer (BOP)stack, generally depicted at 10. The BOP stack comprises a pair of BOPS,shown generally at 14A and 14B. The BOPs are contained within a mainbody 12, which contains a lower tubular 11B for connecting the apparatusto, for example, a riser, and an upper tubular section 11A forconnection to, for example, a lubricator stack.

It will be appreciated that although the drawing shows a dual BOP stack,the BOP can also be used in a single, triple, or other multipleconfiguration.

As most clearly shown in FIG. 4, the BOP stack houses an upper ramassembly 15A and a lower ram assembly 15B, housed in cylindricalcavities oriented in the Y-axis perpendicular to the main wellbore axisZ.

Actuator assemblies 16 and 18 are provided on front and rear sides ofthe apparatus respectively, each actuator assembly including a pair ofhydraulic pistons. In this embodiment, actuator assembly 16 includes onepiston 17A which functions to actuate a ram of assembly 15A, and onepiston 17B functioning to actuate a ram of assembly 15B. Similarly,actuating assembly 18 comprises pistons 19A and 19B, respectivelyfunctioning to actuate opposing rams in ram assemblies 15A and 15B. Ineach case, the pistons are coupled to the rams by scotch yoke typeactuators 13, although it will be appreciated that other arrangementscould be adopted.

Also shown in FIGS. 1 to 4 are equalising spool sub-assemblies 20,located on the diagonal of the body 12. These allow the controlledrelease of well pressure prior to moving the ram assembly from a closedback to an open position. FIGS. 1 to 4 also show 3 injection ports 22allowing fluid to be injected into the cylindrical sections of the BOPstack.

FIG. 4 also shows positioning of the ram assemblies 15A and 15B. In FIG.4, both ram assemblies 15A and 15B are shown in their fully openpositions. The actuation mechanism will be described in more detailbelow.

FIGS. 5A and 5B show components of the ram assembly 15A in more detail.The main body and actuators of the BOP have been removed for clarity.The ram assembly comprises a pair of rams 50, 51, an alignment drum 52,and a ram key plate 54. The individual components of the ram assemblyare shown in FIGS. 6A to 6D.

FIG. 5A shows ram assembly 15A in an open position, whereas FIG. 5Bshows ram assembly 15A in a closed position.

FIG. 6A shows an individual ram 50, having a sealing assembly 60 mountedthereon. The ram 50 comprises a main body 62 which is formed from acylindrical quadrant with main axis Y. In use, the ram rotates about themain cylindrical axis Y. The ram has an interior section removed, toform a part-cylindrical seat 63 for the alignment drum of the ramassembly. The internal radius of the removed section corresponds to theradius of the alignment drum 52, and is approximately 50% of the totalradius of the ram.

The part-cylindrical removed section of the ram 50 does not extend alongthe entire axial length of the ram. The ram comprises an end plate 64,which is received into a corresponding formation 65 in the alignmentdrum.

Formed in the lower edge 66 of the ram is a channel 67 extendingparallel to the main axis Y of the ram assembly. The bore issemi-circular in cross section so that when the lower edge ofcorresponding ram 51 is placed adjacent, a circular throughbore isprovided. The throughbore is arranged to have inner diameter greater orequal to the inner diameter of the wellbore.

Along an opposing, sealing edge 68 of the ram, an additional channel isformed in the main body of the ram, in the axis perpendicular to themain axis Y of the ram assembly and the channel 69 in the opposing edge.The channel is semi-circular such that when the sealing edge of theopposing ram is placed adjacent, a circular aperture (56, FIG. 5B) isformed in the ram pair.

The ram is provided with a seal assembly 60 comprising an outer seal 71and an inner seal 73. The inner and outer seal are elastomeric, and areadapted to seal against a wireline when the rams are in a closedposition. It should be noted that no recess is formed in the inner sealcorresponding to the aperture 56 formed in the ram pair.

FIGS. 6B and 6C show the alignment drum 52 from two differentperspectives. The alignment drum is generally cylindrical, and has aflat end 79 with an axle 80 formed therein. The opposing end of thealignment drum has a section 65 removed. This is a quadrant of axialextent equal to the thickness of the end plate 64 on the ram, andreceives the end plate of a ram when the apparatus is assembled. Members82 are provided for engaging with a spindle of the actuating means.

The alignment drum 52 has a cross-axial bore 81 formed therein. The bore81 is substantially circular in cross section, with diametercorresponding to the inner diameter of the wellbore. In opposing edges83 a, 83 b of the cross-axial bore, channels 84 a and 84 b are formed,extending outwardly from the centre of the cross-axial bore. Thechannels 84 a, 84 b are formed on diametrically opposed sides of thedrum, with a diameter less than that of the cross axial bore 81, butlarge enough to accommodate a wireline or pipeline being run in thewellbore. The channels extend to a distance such that they defineanother cross-axial bore or aperture passing through the central axis ofthe alignment drum. The ends of the channels are rounded to provide asmooth surface for the wireline or pipeline. The edge defined by the rimof the main bore and the rim of the channel is shaped to create asmooth, tapered path from the main bore to the channel. In this example,this is by a pair of tangents inclined to one another at around 90degrees, with smoothed edges where they intersect the channels.

FIG. 6D shows the ram key plate 54, which is formed to an outer diameterequal to that of the alignment drum 52. The ram plate comprises acentral bore 86, which receives the axle 80 of the flat end of thealignment drum 52. The plate 54 is therefore able to rotate with respectto the alignment drum. Members 87 are provided for engaging with aspindle of the actuating means. The plate is a circular disc with aquadrant removed. This quadrant corresponds to the end plate of a ram,and receives the end plate when in the ram assembly.

In its assembled state, the ram assembly is arranged such that thequadrant recess in the alignment drum 52 receives the end plate 64 ofone of the rams, ram 50, such that rotation of the drum effects rotationof the ram, and vice versa. In contrast, the opposing ram 51 is able torotate with respect to the alignment drum 52. However, the ram key plate54, by virtue of its corresponding quadrant will cause the ram 51 to berotated along with the ram key plate 54.

FIGS. 7A and 7B show components of a seal assembly used with anembodiment of the invention. The seal assembly comprises an outer seal71 and an inner seal 73, each comprised of elastomeric materials. Theouter seal 71 is U-shaped in the plane perpendicular to the sealingsurface, and has a curved outer profile 75 shaped to be flush with theouter surface of the ram. Inwardly extending retaining edges 76 areprovided at the prongs of the U. The inner seal 73, which in thisexample is a different material from the outer seal 71, is formed in abroad inverted T-shape. The lower surface 77 of the inner seal 73 abutsa supporting member on the main body of the ram, and the edges 76 of theouter seal fit onto the corners 78 of the inner seal.

The seal arrangement described above is self retaining in the sense thatthe outer seal secures the inner seal to the ram body. In use, when therams are closed to seal the wellbore, the extreme force of the wellpressure will tend to cause the elastomeric inner seals to sticktogether. In the prior art, when moving the ram assembly from a closedposition in which the inner seals of opposing rams are in contact to anopen position in which the rams are separated, the ram blocks will tendto remain in place in the centre of the wellbore unless they aresecurely fitted to the rams. It is conventional to provide metal insertsmoulded in the seals to provide support for screws or bolts used toattach the seal to the ram. In the embodiment of the present invention,the outer seal provides the retention force for the inner seal, removingthe requirement for screws and metal inserts. This simplifies theprocess for manufacturing the seals, which may be by a simple injectionmoulding process.

In the start position, shown in FIG. 4, the pair of rams occupies thelower half of the cylindrical cavity in the BOP body. In this position,the cross axial bore of the alignment cylinder is aligned with wellbore.In addition, the bore defined by the semicircular channels 67 in thelower edges of the rams is in alignment with the main wellbore, and therams are in an open position.

In use, with reference to FIGS. 1 and 4, the piston 17A is actuated,causing rotation of the scotch yoke type actuator, which is coupled tothe alignment drum. This effects rotation of the alignment drum 90degrees in an anti-clockwise sense from the perspective of FIG. 1.Simultaneously, the corresponding piston 19 a on the rear face isactuated and causes rotation of the ram plate. The cooperating quadrantformation engages with the ram causing the ram to be rotated 90 degreesin a clockwise sense from the perspective of FIG. 1.

After actuation, the two rams occupy the volume of the top half of thecylindrical cavity in the BOP body. In this position, the sealing edges68 of the ram are located together. The outer seals 71 seals around theedge between the body of the cavity and the main wellbore, and the innerseals 73 seal against the wireline or pipeline extending through thewellbore. The shape of the seal assembly is such that the apparatus isself-energising, as well pressure tends to force the seals upward andinwards, causing the seal to be maintained.

FIGS. 8A to 8D show the operation of the embodiment of FIGS. 5 and 6 inmore detail, and in particular show the function of the alignment drum.

FIG. 8A is a plan view of the ram assembly in its open position. In thisposition, the rams 50, 51 occupy the bottom half of the cylindricalcavity in the BOP body. The Figure shows the throughbore 81 fullyaligned with the wellbore. In addition, the semi circular channels 67formed in the lower edges of the rams provide full clearance of the ramsfrom the wellbore. The wireline 89 extends through the bore defined bythe cross axial bore in the alignment drum and the semi-circularrecesses in the lower edges of the rams. In practice, the wireline isunlikely to be perfectly central in the bore.

FIG. 8B shows the ram assembly partially through its rotation cycle,approximately 50% through rotation. Here, the alignment drum has rotatedthrough around 45 degrees, and the sealing faces of the rams areinclined at approximately 90 degrees to one another. The wirelineextends through the aperture defined by the bore and channels formedeither side of the bore, which is now in the shape of a square, rotatedthough 45 degrees, with an elongate channel extending across thediagonal of the square, formed from the channels 84 a and 84 b andaligned with the cut-out formations in the sealing edges of the ram.

As the alignment drum continues to rotate in the direction of the arrow,the aperture in which the wireline resides becomes progressivelysmaller, and the wireline is guided towards the centre of the bore andthe locating channels 84 a, 84 b. The guiding edges of the bore areshaped to provide a smooth path for the wireline. It is notable that thewireline is guided by the upper guiding edge of the bore, and by thelower guiding edge of the bore simultaneously. This is in contrast to aconventional ram-type BOP, in which the one guiding means on one of therams moves before the other.

FIG. 8C shows the ram assembly almost fully in its closed position. Inthis position, the rotated square aperture is no longer present, and theaperture is an elongate locating channel aligned with the cut-outformations in the sealing edges of the ram.

FIG. 8D shows the ram assembly in its fully closed position.

FIGS. 9A and 9B show an alternative embodiment of the invention, inwhich the alignment drum 91 has shape different from that in theembodiment of FIGS. 5 and 6.

In this example, the invention is implemented as a shear and seal BOP,used when the wireline needs to be cut to release the tool string below.The shearing alignment drum shown in FIGS. 9A and 9B differs from thealignment drum of FIGS. 6A and 6B in that a locating channel 94 is onlyprovided in one edge of the bore in the alignment drum 91, which becomesthe lower edge as the drum rotates towards the closed position. Thislower edge functions to guide the wireline towards the centre of thebore.

In place of the upper locating channel on the opposing edge, a roundedcutting edge 92 is formed at the intersection of guiding edges. In thisexample, the guiding edges are two tangents to the bore edges, inclinedto one another at around 90 degrees.

FIGS. 10A and 10B show a ram assembly 100 including the alignment drum91 at different stages in the rotation cycle. The wireline, guided tothe centre of the bore by the lower guiding edges is met by the cuttingedge 92 before the drum is fully through its rotation cycle. As the ramassembly proceeds to the fully closed position, the cutting edge shearsthrough the wireline. The wellbore is sealed by the sealing assembly, asdescribed above.

The present invention offers numerous improvements over previouslyproposed valves.

Firstly, embodiments of the invention introduce a component of themovement of rams in the vertical, rather than lateral dimensions. In theembodiment described, this is achieved by using a circular movement ofthe rams used to close a conduit. By “wrapping around” the movement ofthe rams, the lateral extension of the valve components is significantlyreduced.

The reduction in lateral dimensions over conventional ram-type BOPsvaries according to operating pressure of the BOP and diameter of thewellbore.

For 3 inch diameter wellbore, a 10,000 PSI BOP would be expected to havea maximum lateral dimension of around 30 cm, compared with 110 cm for aconventional ram-type BOP.

For 6 inch diameter wellbore, a 10,000 PSI BOP would be expected to havea maximum lateral dimension of around 60 cm, compared with 190 cm for aconventional ram-type BOP.

In another example, the largest lateral dimension of a BOP stack of thetype described is less than 75 cm, compared with around 2.5 meters in anequivalent ram-type BOP.

In the example shown in FIGS. 1 to 3, the maximum lateral dimension,including hydraulic actuators, is around 40 cm.

These dimensions are less than half, and indeed less than a third, ofthe dimensions of the equivalent conventional ram-type BOP.

This improves the manoeuvrability of the apparatus, and allows it to belowered in, around and through platforms on the rig. Significantly, theBOPs may be installed much closer to the wellhead, having positiveeffects on the height available for the lubricator stack and the toolstring.

The present invention also provides apparatus of reduced weight whencompared with conventional ram-type BOPs, which further improvesmanoeuvrability.

In addition, the ram assembly design is significant in that the ramsmove from an open to a closed position without changing the volume ofcomponents at well pressure. The cylindrical cavities in which the ramassemblies are located are at well pressure when the apparatus is in itsopen position. When actuated, there is no requirement to forcepiston-connecting rods into the well volume, in contrast to theconventional ram-type BOP. This feature of conventional BOPs means thatthere is a requirement to overcome well pressure, which can only beachieved by significant force.

In manually actuated BOPs this requires large screws and large levers inorder for the operator to generate enough torque, and this places a hugeburden on the operator. In hydraulically actuated systems, there is arequirement for large diameter cylinders, which increases the weight andsize of the apparatus. During operation of the present invention, thevolume swept by the rams does not change, and the result is that lessforce is required to actuate the rams. This means that smaller diameterhydraulic actuators can be used. In addition, manually actuated systemsare more feasible using the present design. In both manually andhydraulically actuated apparatus, the time taken to close the wellboreis greatly reduced, improving the safety at the rig.

The reduced requirement for hydraulics reduces the need to provide screwlocking mechanisms which are typically used in conventional ram-typeBOPs to manually secure the rams in their closed configuration afteractuation by the hydraulics. In the present design, the apparatus couldbe locked in one position by a simple peg and hole arrangement in theactuating mechanism and the main body of the BOP stack.

The manner in which the apparatus is constructed is simple, and allowssimple installation and stripping down by removal of two plates on oneside of the apparatus.

The construction of the apparatus allows convenient location ofequalisation channels and injection channels, without conflicting withscrews and fittings.

The alignment drum offers a number of advantages over conventionalram-type BOPs.

In the present embodiment, the rams are fully supported around theentire outer surface of the rams. The alignment of the wireline orpipeline is not done by any component of the rams themselves, and thuscompromising the strength of the rams by providing recesses on thesupporting surface is not necessary.

Alignment of the wireline is by the profiles of the upper and lower edgeof the cross axial bore of the drum. The alignment is therefore at twospatially separated locations on the wireline, reducing the likelihoodof damage or snagging of the wireline during closing.

In addition, the movement of the guiding edges against the wireline issuch that the edges move across the wire while moving a small distancealong the wireline as the drum rotates. The force is therefore impartedover a short range of points, rather than being a slicing effect at asingle point of the wire. This further reduces the tendency of thewireline to snag.

The movement of the alignment drum to the closed position provides twoguiding edges for the wireline, moving in opposite senses, which bytheir nature must act in concert, as opposed to the guides in theconventional ram-type BOP which are likely to move separately, reducingtheir effectiveness.

References to wireline applications should not be taken as limiting. Theabove described apparatus is suitable for sealing a conduit around anywireline, slickline, pipeline, umbilical or cable. Indeed, the apparatushas certain advantages for general valves, even where there is norequirement to seal around an internal line.

Various modifications and improvements may be made to theabove-described embodiments within the scope of the invention hereinintended.

1. Apparatus for sealing a wellbore, the apparatus comprising a ramassembly having a pair of rams mounted in a housing, the rams rotatableabout a common axis of rotation, wherein the apparatus has a first openposition in which fluid may pass through the wellbore and a secondclosed position in which the rams abut to seal the wellbore, and whereinthe apparatus is adapted to be moved between the open and closedpositions by rotating the rams about their common axis of rotation,wherein the apparatus further comprises alignment means for guiding awireline or pipe towards the centre of the wellbore during rotation ofthe rams, and wherein the alignment means is a drum adapted to rotateabout an axis of rotation of the rams.
 2. Apparatus as claimed in claim1, wherein each ram is adapted to rotate about an axis perpendicular toa longitudinal axis of the wellbore.
 3. Apparatus as claimed in claim 1,wherein the rams are adapted to be moved between the open and closedpositions by rotating the rams in opposite senses.
 4. Apparatus asclaimed in claim 1, wherein the apparatus has a maximum lateraldimension of 80 cm.
 5. Apparatus as claimed in claim 1, wherein amaximum lateral dimension is less than 50 cm.
 6. Apparatus as claimed inclaim 1, wherein a maximum lateral dimension is less than 40 cm. 7.Apparatus as claimed in claim 1, wherein the rams comprise locatingformations for locating a wireline or pipe when in the closed position.8. Apparatus as claimed in claim 1, wherein the drum is keyed with oneof the rams and rotates with said ram.
 9. Apparatus as claimed in claim1, wherein the drum comprises a throughbore through which the wirelineor pipe extends.
 10. Apparatus as claimed in claim 9, wherein thethroughbore defines an aperture extending in a longitudinal axis of thewellbore, arranged such that the aperture decreases in cross sectionalarea during rotation of the drum.
 11. Apparatus as claimed in claim 9,wherein the throughbore is perpendicular to the axis of rotation of thedrum.
 12. Apparatus as claimed in claim 9, wherein a first opening ofthe throughbore is provided with a channel formed outwardly from an edgeof the throughbore.
 13. Apparatus as claimed in claim 12, wherein asecond opening of the throughbore is provided with an edge formationdiametrically opposed from the channel.
 14. Apparatus as claimed inclaim 13, wherein the edge formation is a second channel formedoutwardly from an edge of the throughbore, such that the first andsecond channels together form an aperture extending through the drumperpendicular to the axis of rotation.
 15. Apparatus as claimed in claim14, wherein the aperture extends longitudinally in the wellbore and iscentral in the wellbore when the apparatus is in its closed position.16. Apparatus as claimed in claim 13, wherein the edge formation is acutting edge adapted to shear a wireline or pipe as the apparatus movesto its closed position.
 17. Apparatus as claimed in claim 1, whereineach ram comprises a sealing assembly having one or more elastomericseals.
 18. Apparatus as claimed in claim 17, wherein each sealingassembly comprises an inner seal adapted to cooperate with an inner sealon the opposing ram to seal against the wireline or pipe.
 19. Apparatusas claimed in claim 18, wherein the sealing assembly comprises an outerseal adapted to seal edges of the wellbore against well pressure. 20.Apparatus as claimed in claim 19, wherein the inner seal is retained onthe ram by the outer seal.
 21. Apparatus for sealing a wellbore around awireline or pipe being run in the wellbore, the apparatus comprising: aram assembly having a pair of rams mounted for rotation about a commonaxis of rotation; wherein the apparatus has a first osition in which thewellbore is open and a second position in which the wellbore is closed;and wherein the actuating means is adapted to cause the rams of the ramassembly to rotate about their common axis of rotation from a positionin which the apparatus is in its first open position, to a position inwhich the apparatus is in its second closed position in which thewellbore is sealed around the wireline or pipe, wherein the pair of ramsare rotatably mounted in a housing of the apparatus, wherein theapparatus further comprises alignment means for guiding a wireline orpipe towards the centre of the wellbore during rotation of the rams, andwherein the alignment means is a drum adapted to rotate about the axisof rotation of a ram.
 22. Apparatus as claimed in claim 21, wherein theram comprise formations for locating a wireline or pipe in the closedposition.
 23. Apparatus for sealing a wellbore, the apparatus comprisinga pair of rams which are rotatable about a common axis of rotationbetween a first position in which the wellbore is open and a secondposition in which the rams seal the wellbore around a wireline or pipe,characterized in that when the apparatus is in its operatingorientation, the apparatus has a maximum lateral dimension which allowsit to pass through an aperture in a rig platform through which thewellhead control equipment passes, wherein the rams are rotatablymounted in a housing of the apparatus, and wherein the alignment meansis a drum adapted to rotate about the axis of the rams.
 24. Apparatus asclaimed in claim 23, wherein the maximum lateral dimension is less than80 cm.
 25. Apparatus as claimed in claim 23, wherein the maximum lateraldimension is less than 50 cm.
 26. Apparatus as claimed in claim 23,wherein the maximum lateral dimension is less than 40 cm.
 27. Apparatusas claimed in claim 23, wherein the rams comprise formations forlocating a wireline or pipe in the closed position.
 28. Apparatus asclaimed in claim 23, wherein the apparatus further comprises alignmentmeans for guiding a wireline or pipe towards the centre of the wellboreduring rotation of the rams.
 29. Apparatus for sealing a wellbore, theapparatus comprising a pair of rams which are rotatable about a commonaxis of rotation between a first position in which the wellbore is openand a second position in which the rams seal the wellbore around awireline or pipe, characterised in that when the apparatus is in itsoperating orientation, the apparatus has a maximum lateral dimension ofless than 80 cm, wherein the rams comprise formations for locating awireline or pipe in the closed position, wherein the apparatus furthercomprises alignment means for guiding a wireline or pipe towards thecenter of the wellbore during rotation of the rams, and wherein thealignment means is a drum adapted to rotate about the axis of rotationof the rams.
 30. Apparatus for sealing a wellbore, the apparatuscomprising: a ram assembly having a pair of rams, mounted for about acommon axis of rotation; and actuating means; the apparatus having afirst open position in which fluid may pass through the wellbore and asecond closed position in which the rams abut to seal the wellbore; andwherein the rams are adapted to be moved from the first and secondpositions without substantially changing the volume of the actuatingmeans exposed to well pressure, wherein the rams are rotatably mountedin the housing of the apparatus, wherein the apparatus further comprisesalignment means for guiding a wireline or pipe towards the center of thewellbore during rotation of the rams, and wherein the alignment means isa drum adapted to rotate about the axis of rotation of the rams. 31.Apparatus as claimed in claim 30, wherein the rams comprise formationsfor locating a wireline or pipe in the closed position.
 32. Apparatusfor sealing a wellbore, the apparatus comprising: a ram assembly havinga pair of rams rotatably mounted in a housing, apparatus having a firstopen position in which fluid may pass through the wellbore and a secondclosed position in which the ram abut to seal the wellbore, wherein theapparatus is adapted to be moved between the open and closed position byrotating the rams; and a drum adapted to rotate about an axis ofrotation of the rams, for the guiding a wireline or pipe towards thecenter of the wellbore during rotation of the rams.
 33. Apparatus forsealing a wellbore, the apparatus comprising: a ram assembly having apair of rams rotatably mounted in the housing; actuating means; and adrum adapted to rotate about an axis of rotation of the rams; whereinthe apparatus has a first open position in which fluid may pass throughthe wellbore and a second closed position in which the rams abut to sealthe wellbore; and wherein the rams are adapted to be moved between thefirst and second positions by rotating the rams without substantiallychanging the volume of the drum exposed to well pressure; and furtherwherein the drum is for guiding a wireline or pipe towards the centre ofthe wellbore during rotation of the rams.